THECOSMICMICROWAVEBACKGROUND ANDPARTICLEPHYSICS

Abstract

In forthcoming years, connections between cosmology and particle physics will become increasingly important with the advent of a new generation of cosmic microwave background (CMB) experiments. Here, we review a number of these links. Our primary focus is on new CMB tests of inflation. We explain how the inflationary predictions for the geometry of the Universe and primordial density perturbations will be tested by CMB temperature fluctuations, and how the gravitational waves predicted by inflation can be pursued with the CMB polarization. The CMB signatures of topological defects and primordial magnetic fields from cosmological phase transitions are also discussed. Furthermore, we review current and future CMB constraints on various types of dark matter (e.g. massive neutrinos, weakly interacting massive particles, axions, vacuum energy), decaying particles, the baryon asymmetry of the Universe, ultra-high-energy cosmic rays, exotic cosmological topologies, and other new physics.

Signatures of short distance physics in the cosmic microwave background

“…But in light of the bound H < 7 × 10 13 GeV on the Hubble scale of inflation [28], we see that the modular inflation models with n > 2 are excluded already, and we can ignore them henceforth.…”

Magnetogenesis and the dynamics of internal dimensions

“…The magnetic energy density can be obtained by tracing over the physical polarizations with the result that 18) where, 19) is the logarithmic energy spectrum of the magnetic fluctuations [16,17] expressed in terms of the comoving wavenumber k which equals the physical momentum of the wave at η = −η 1…”

The cosmic microwave background radiation

“…This lends credence to the interpretation of the observed anisotropies as the result of density perturbations which seeded the formation of galaxies and clusters. The discovery of temperature anisotropies by COBE provides evidence that such density inhomogeneities existed in the early universe, perhaps caused by quantum fluctuations in the scalar field of inflation or by topological defects resulting from a phase transition (see Kamionkowski & Kosowsky, 1999 for a detailed review of inflationary and defect model predictions for CMB anisotropies). Gravitational collapse of these primordial density inhomogeneities appears to have formed the large-scale structures of galaxies, clusters, and superclusters that we observe today.…”

“…Scalar (density) perturbations generate curl-free (electric mode) polarization only, but tensor (gravitational wave) perturbations can generate divergence-free (magnetic mode) polarization. Hence the polarization of the CMB is a potentially useful probe of the level of gravitational waves in the early universe Kamionkowski & Kosowsky, 1998), especially since current indications are that the large-scale primary anisotropies seen by COBE do not contain a measurable fraction of tensor contributions . A thorough review of gravity waves and CMB polarization is given by Kamionkowski & Kosowsky (1999).…”